Russian warships heading for Syria could be used to target civilians in the besieged city of Aleppo, NATO Secretary-General Jens Stoltenberg warned yesterday as he called on Moscow to implement a lasting ceasefire.

The warning came as the Russian task force sailed toward the Strait of Gibraltar, where it was expected to arrive late yesterday or early today. At least two of the vessels are also expected to stop in Ceuta to refuel.

“Spain signed EU statement on Russian war crimes in #Aleppo last week,” he tweeted yesterday to his 96,692 followers.

“Today helps refuel fleet on way to commit more atrocities. Seriously?”

News of the planned Ceuta pitstop generated controversy late last night, with media in the UK and Spain running stories reflecting NATO’s concern at Spain’s actions.

Sir Gerald Howarth, a former defence minister, told the Telegraph it would be “wholly inappropriate” for a Nato member to refuel the vessels.

Former Royal Navy chief Lord West told the newspaper: “There are sanctions against Russia and it’s an extraordinary thing for a Nato ally to do.”

Last night Spain’s Ministry for Foreign Affairs said requests from the Russian navy were considered on a “case by case basis, depending on the characteristics of the ship concerned”.

“Russian navy vessels have been making calls in Spanish ports for years,” a ministry spokesman said.

But there was a clear indication too that Madrid was feeling the pressure from the international community.

“The latest requested calls are currently being reviewed in light of information we are receiving from our allies and from the Russian authorities,” the spokesman said.

Spain’s caretaker defence minister, Pedro Morenés, also told reporters the government would seek clarification from Russia about “the purpose and destination” of the ships.

A UK Government spokesman said: “Access to Spanish ports is a matter for the Spanish authorities. HMG has previously expressed concerns to the Spanish government about its hospitality to the Russian navy when we have concerns about Russia’s military activity.”

“We are clear that the UK’s relationship with Russia should not be business as usual.”

Last week’s Russian passage through the Channel came after Theresa May condemned Vladimir Putin’s aggression in Syria, accusing Moscow of being behind “sickening atrocities” in support of Bashar Assad’s regime.

Nato said the prospect of Russia’s only aircraft carrier heading to the region does not “inspire confidence” that Moscow is seeking a political solution to the Syrian crisis.

Russian defence minister Sergei Shoigu said in September that the Admiral Kuznetsov-led Northern Fleet would be joining a taskforce in the Mediterranean.

According to the Russian news agency Tass, he told a defence board meeting that the plan was to bolster the Mediterranean fleet’s “combat capabilities”.